Methods and apparatus for paper testing

ABSTRACT

The specification discloses methods and apparatus to test the tendency of paper surfaces to be disrupted by the materials and forces applied to the paper during the printing process.

United States Patent Lyon et al. Jan. 29, 1974 METHODS AND APPARATUS FOR PAPER [56] References Cited TESTING UNITED STATES PATENTS [75] Inventors: William B. Lyon, Bethel Park; 2,705,424 4/1955 Pomper 73/150 William D. Schaeffer, OHara Townshlp Allegheny County Primary Examiner-Richard C. Queisser twill-of 1 Assistant Examiner-Denis E. Corr [73] Assignee: Graphic Arts Technical Foundation, Attorney, Agent, FirmBuell1 Blenko &

Pittsburgh, Pa. Ziesenheim [22] Filed: Feb. 14, 1972 [57] ABSTRACT [21] Appl. No.: 225,890

The spec1ficat1on dlscloses methods and apparatus to test the tendency of paper surfaces to be disrupted by [52] U.S. Cl. 73/159, 73/150 the materials and forces applied to the paper during 51 1m. (:1. G0ln 19/04 the priming prom, [58] Field of Search 73/159, 150, 7

Adjustmem Means 8 Claims, 4 Drawing Figures Adjustment Means METHODS AND APPARATUSFOR PAPER TESTING This invention relates to a machine and process to test discrete properties of paper inorder that performance during printing maybe predicted.

Paper used in lithographic offset printing or variations thereof is subjected to various forces and exposed to various materials during the course of the printing process which tend to disrupt the paper surface. Excessive surface disruption can result in delamination or rupture of the surface or result in paper fibers being displaced onto the printing blanket. Accordingly, the paper used in such processes must possess certain characteristics to be suitable for such use.

In letterset, dry offset, or Driographic printing, the ink is transferred from the surface of the printing plate mounted on a first cylinder to a rubber blanket mounted on an intermediate cylinder. The ink is transferred in turn to the paper under the pressure of a third cylinder, the impression cylinder. Simple rolling contact between the blanket and impression cylinder does not provide adequate pressure for proper transfer of the ink to the paper. Therefore the cylinder carrying the blanket and impression cylinder are overpacked to provide a positive interference between the blanket and impression cylinders. The compression between the blanket and impression cylinder causes a flow of the blanket away from the area of minimum clearance and toward the entrance to and exit from the printing nip resulting in compression of the paper. The compression of the blanket thus causes relative movement of the blanket while in contact with the paper and produces a small but significant shear in the immediately adjacent and contacting paper surface. The contact can also result in adhesion of specific surface elements of the paper to the blanket. These elements can be displaced to the blanket surface in the exit of the nip where the blanket and paper follow divergent paths and the ink film is split. The forces result in a picking of the paper. Displaced paper fibers are usually referred to as lint; whereas paper surface elements which are raised without being displaced to the blanket surface are referred to as fluff.

Paper utilized for either direct or offset lithography is exposed to a fountain solution. The primary function of the fountain solution is to provide image fidelity and maintain the definition of image and non-image areas during both types of printing. In direct lithography the ink on the image areas of the plate and fountain solution on the non-image areas are transferred directly to the paper under the force imposed by the impression cylinder. In the case of off-set lithography the ink and fountain solution are transferred from the plate to the rubber blanket covered cylinder during each revolution and in turn are transferred either to a paper sheet or .web in the nip formed with the impression cylinder.

Printing papers, coated papers in particular, differ markedly in their receptivity for aqueous fountain solutions. Differences are displayed with respect to wettaimportant in the printing of coated papers on multicolor presses on which the time required'for passage of paper between printing units can be of the same order of magnitude as the time involved for the fountain solution to soften the coating. As a result the paper passing through the second and subsequent printing units when subjected to the shear or rubbing of the blankets may be especially susceptible to having surface elements displaced to the blanket surface in the exit of the nip.

Particulate elements such as lint may become mixed with ink on the blanket and the mass is referred to as blanket pile. A continuous film may be built upon the blanket derived from materials extracted from the paper, e.g., coating clay, Such a film is known as milk.

As can be seen the various printing processes impose a wide variety of requirements upon the paper stocks employed. Some of the requirements such as pick resistance, are common to many processes; some, such as lithographic milking, are pertinent to particular processes. In addition, the levels of the forces imposed on the papers are altered significantly by operational variables and printing job variables. Increased printing speed increases the splitting force imposed on the paper by the ink. Increased ratio of non-image to image area increases the fountain solution to ink ratio in the printing nip. The papers capability to withstand these forces will vary both from side to side and with direction.

Paper produced for printing has to be tested by the manufacturer in order to predict the performance of the paper. A direct test may be made by a press run. Use of a press run for testing requires a substantial capital investment. Since some of the deficiencies in paper stock such as formation of blanket pile and milking are cumulative, a very large quantity of paper must be run through the press in order to obtain a significant test. Such tests are therefore necessarily time consuming and expensive.

A variety of small scale tests have been proposed with the intention of obtaining reliable results from testing in a laboratory. Many of these tests have been unsatisfactory and of dubious reliability. Many of the tests had to be performed manually. In some cases the tests were of little value due to the small area of the paper surface contacted, the static nature of the test or excessive moisture being applied. No single apparatus existed to perform the several tests necessary to evaluate the characteristics of paper stock related to its receptivity for moisture and its resistance to rubbing and abrasion when in contact with an elastomeric surface.

We have overcome the above-mentioned problems of paper testing. We provide a paper testing apparatus and process in which sheet paper specimens may be tested for pick resistance, fluid resistance and the like. We provide cylinder means revolvable upon its axis, wheel means revolvable upon its axis, and drive means in operative connection with the cylinder means. We mount a paper specimen to be tested on the cylinder means and an elastomeric blanket on the wheel means. The cylinder means and the wheel means are mounted to provide for relative movement of their axes toward and away from each other. We prefer to provide fluid I dispensing means positioned to selectively dispense fluid upon a portion of the paper specimen. We prefer to provide control means operable to regulate the speed of the drive means. We furthervpreferably provide traverse means operable to provide relative axial movement between the cylinder means and the wheel means. We may additionally provide second wheel means mounted on an axis parallel to the axis of the cylinder means.

Other details, objects and advantages will become more apparent as the following description of a present preferred embodiment of the invention proceeds. A present preferred embodiment of the invention is shown in the accompanying drawings in which:

FIG. 1 is a plan view of testing apparatus embodying the invention;

FIG. 2 is an end elevational view of the apparatus shown in FIG. 1;

FIG. 3 is an enlarged view of a portion of the specimen cylinder of FIG. 2, showing one way of fastening a paper specimen to the cylinder; and

FIG. 4 is an end elevational view similar to the apparatus in FIG. 2 but with second wheel means rotatably mounted on an axis parallel to the axis of the cylinder and operably engaged with the paper specimen mounted thereon to selectively deposit fluid on the paper specimen.

The apparatus (FIGS. 1 and 2) includes a cylinder I mounted on an axle 2 which is arranged for rotation in bearings which have been omitted for simplicity of illustration. The axle is revolved by a motor 3 connected to a motor speed control 4 by wires 5. A wheel 6 is mounted on axle 7 joumalled in bracket 8 parallel to axle 2. Bracket 8 is mounted on lower bracket 9 for movement toward and away from cylinder 1. Lower bracket 9 threadably engages screw 10 and is movable parallel to cylinder 1 by rotation of screw 10.

The mounting of cylinder 1 and wheel 6 is comparable to an engine lathe in which cylinder 1 is mounted in the head-stock and wheel 6 is mounted in the tool holder.

A paper specimen 11 may be placed circumferentially around cylinder 1 for testing. The ends are placed in a slot 12 running longitudinally of cylinder 1 and are locked in place by driving a wedge 13 (FIG. 3) into slot 12. An elastomeric tape 14 is placed around the circumference of wheel 6. 3M Scotch-Mount Tape Y- 9130A (Catalog No. 4416) black closed cell vinyl twosided tapes have been found satisfactory.

A pen 15 including a stylus 16 is mounted above cylinder 1 upon a support bar 17. Bar 17 is mounted on a pivot 18 for movement of pen 15 toward and away from cylinder 1. A counterweight 19 is adjustably placed on support bar 17 to enable the downward pressure of pen 15 to be regulated. Pivot 18, support bar 17, and pen 15 are mounted on an extension (not shown in the drawings) from lower bracket 9. A Kohinoor No. 3065 Rapidograph pen with a No. 3 stylus has been found satisfactory.

In the embodiment shown in FIG. 4 a second wheel 20 is adapted to receive a circumferential elastomeric tape or tire 21. The elastomeric material mounted on wheel 20 is not a tacky material as used on wheel 6 but is, instead, harder and approximates the material used for a printing blanket. Wheel 20 is journalled in a bracket 22 which is carried upon an extension (not shown in the drawings) from the tool bracket. Wheel 20 may also be moved toward and away from cylinder 1 in the same manner as wheel 6.

The apparatus can be employed to carry out a variety of tests upon paper specimens. One such test is a dry pick test which will test the resistance of dry paper against linting. Wheel 6 is advanced toward cylinder 1 until there is contact between paper specimen 11 and elastomeric tape 14. Then wheel 6 is further advanced a measured amount to provide a controlled interference and nip between the blanket and the paper. An interference of 0.0040 i 0.0005 inches may be satisfactory for an initial test. Cylinder 1 is then driven by motor 3. As it revolves, wheel 6 will also revolve, being driven by frictional contact. Tape 14 will be deformed in the nip causing scuffing of the paper and tending to produce lint. The lint will be picked up by the tape where the movement may be measured or counted. The amount of lint may be measured for a given number of revolutions of cylinder 1, or the number of revolutions of cylinder 1 required to produce a given amount of lint may be measured. The interference and speed may be varied to introduce other variables which are significant in a printing operation. Screw 10 may also be caused to rotate at a speed proportioned to the speed of cylinder 1. Elastomeric tape 14 will then trace a helical path obtaining a long length of rolling contact on a relatively small paper specimen.

It is often desirable to introduce a certain amount of slip in the nip to increase scuffing forces upon the paper and to measure rub resistance. A motor 23 is mounted on axle 7. Motor 23 may be used to drive tape 14 at a faster peripheral speed that paper specimen 11 or it may be used as a dynamic brake to retard rotation of the tape. The induced slip should be precisely controlled and measured. Any convenient form of control apparatus may be used to control the slip and some form of digital counter for cylinder 1 and wheel 6 has been found satisfactory for measuring purposes.

A fluid absorption test may be made by making pen l5 operative in the test. The pen is filled with an aqueous solution whose composition may be adjusted to obtain desirable attributes of surface tension, viscosity, and the like. Wheel 6 is backed off from cylinder 1, pen 15 is moved toward the paper specimen and cylinder 1 is revolved. Pen 15 may be caused to trace a helical path by revolving screw 10 as cylinder 1 revolves. By measuring the amount of fluid in the pen, at the beginning and end of the test (e.g., by weight) and by knowing the length of the path traced by the pen (a function of the number of revolutions of cylinder 1) a measure of the paper's fluid receptivity is given. The size of the pen stylus and its downward pressure upon the paper specimen may be adjusted to give varying conditions. Likewise the speed of cylinder 1 may be adjusted.

A wet pick or piling test may be conducted by bringing elastomeric tape 14 into interference with the paper specimen 1 I mounted on cylinder 1 while pen l5 delivers fluid. Thus, the paper specimen upon which fluid is deposited will shortly be engaged in the nip with tape 14. The amount of lint collected can be measured in the same manner as previously. The other variables may also be adjusted to simulate different press conditions.

It may be desirable to simulate the distribution of a solution on paper by a printing blanket. In such a case a wheel 20 with a tape or tire 21 is introduced between pen 15 and cylinder 1. Fluid is deposited on the paper specimen 11 by means of elastomeric tape 21. Paper specimen 1 l is then brought into interference with tape 14 and tests may be carried out in the same fashion as previously described.

As can be seen from the foregoing description we have provided apparatus and processes to perform a wide variety of tests to determine how a particular paper stock will behave during its use in printing. The tests can be performed quickly and inexpensively without the necessity of using large quantities of paper or tying up production presses. Furthermore, the tests are performed on a single apparatus which closely simulates actual press conditions and provides valid test results.

We claim:

1. Apparatus for paper testing comprising:

a. cylinder means revolvable upon the axis thereof and adapted to receive a paper specimen on the outer surface thereof,

b. power means in driving connection with said cylinder, 1

c. wheel means adjacent the cylinder means, revolvable upon the wheel axis, and adapted to receive a tacky elastomeric substance upon the wheel surface, and

d. support means for said wheel means adjustable toward and away from said cylinder means whereby contact and pressure between a tacky elastomeric substance and the paper specimen may be increased and decreased.

2. The apparatus of claim 1 wherein screw means are in driving connection with the wheel means support and operable to advance the wheel means parallel to the axis of the cylinder means.

3. The apparatus of claim 1 wherein fluid applicator means are mounted adjacent the cylinder means for application of fluid to the specimen during rotation of the cylinder means.

4. Apparatus for paper testing comprising:

a. cylinder means revolvable upon the axis thereof and adapted to receive a paper specimen on the outer surface thereof,

b. power means in driving connection with said cylinder,

c. wheel means adjacent the cylinder means, revolvable upon the wheel axis, and adapted to receive paper picking means upon the wheel surface,

d. support means for said wheel means adjustable toward and away from said cylinder means whereby contact and pressure between the paper picking means and the paper specimen may be increased and decreased,

e. second wheel means adjacent the cylinder means revolvable upon the wheel axis,

f. fluid receiving means mounted on the outer surface of the second wheel means,

g. second wheel means adjustable toward and away from the cylinder means whereby contact and pressure between the fluid receiving means and the paper specimen may be increased and decreased, and

h. fluid applicator means mounted adjacent the second wheel means for application of a fluid to the fluid receiving means during rotation of the second wheel means.

5. The apparatus of claim 4 wherein screw means are in driving connection with the wheel means support and operable to advance the wheel means parallel to v the axis of the cylinder means.

6. The apparatus of claim 4 wherein motor means are operably connected to said wheel means and said second wheel means.

7. The method of testing paper for resistance to picking, linting and the like which comprises:

a. mounting a sheet paper specimen around the circumference of a cylinder,

b. providing a wheel with an elastomeric tire adjacent the surface of the cylinder,

c. advancing the wheel toward the cylinder until a measured interference exists between the tire and the paper specimen,

d. revolving the cylinder at measured speed,

e. determining the extent of rolling contact between the tire and paper specimen, and

f. measuring the amount of paper fiber deposited on the tire.

8. The method of claim 7 wherein a fluid is deposited on the surface of the paper specimen. 

1. Apparatus for paper testing comprising: a. cylinder means revolvable upon the axis thereof and adapted to receive a paper specimen on the outer surface thereof, b. power means in driving connection with said cylinder, c. wheel means adjacent the cylinder means, revolvable upon the wheel axis, and adapted to receive a tacky elastomeric substance upon the wheel surface, and d. support means for said wheel means adjustable toward and away from said cylinder means whereby contact and pressure between a tacky elastomeric substance and the paper specimen may be increased and decreased.
 2. The apparatus of claim 1 wherein screw means are in driving connection with the wheel means support and operable to advance the wheel means parallel to the axis of the cylinder means.
 3. The apparatus of claim 1 wherein fluid applicator means are mounted adjacent the cYlinder means for application of fluid to the specimen during rotation of the cylinder means.
 4. Apparatus for paper testing comprising: a. cylinder means revolvable upon the axis thereof and adapted to receive a paper specimen on the outer surface thereof, b. power means in driving connection with said cylinder, c. wheel means adjacent the cylinder means, revolvable upon the wheel axis, and adapted to receive paper picking means upon the wheel surface, d. support means for said wheel means adjustable toward and away from said cylinder means whereby contact and pressure between the paper picking means and the paper specimen may be increased and decreased, e. second wheel means adjacent the cylinder means revolvable upon the wheel axis, f. fluid receiving means mounted on the outer surface of the second wheel means, g. second wheel means adjustable toward and away from the cylinder means whereby contact and pressure between the fluid receiving means and the paper specimen may be increased and decreased, and h. fluid applicator means mounted adjacent the second wheel means for application of a fluid to the fluid receiving means during rotation of the second wheel means.
 5. The apparatus of claim 4 wherein screw means are in driving connection with the wheel means support and operable to advance the wheel means parallel to the axis of the cylinder means.
 6. The apparatus of claim 4 wherein motor means are operably connected to said wheel means and said second wheel means.
 7. The method of testing paper for resistance to picking, linting and the like which comprises: a. mounting a sheet paper specimen around the circumference of a cylinder, b. providing a wheel with an elastomeric tire adjacent the surface of the cylinder, c. advancing the wheel toward the cylinder until a measured interference exists between the tire and the paper specimen, d. revolving the cylinder at measured speed, e. determining the extent of rolling contact between the tire and paper specimen, and f. measuring the amount of paper fiber deposited on the tire.
 8. The method of claim 7 wherein a fluid is deposited on the surface of the paper specimen. 